England’s average temperature is much lower than most parts of Australia. Your population is more than double Australia’s, in a landmass significantly smaller than Australia. You live next to a continent of half a billion people who have to deal with extreme’s of cold. The Pound is worth nearly double the Australian dollar.

Given all the above, it is no surprise that double glazing is much cheaper to install in England than Australia. So most people here just put up with the 3-5mm panes of glass installed in their houses by default.